For decades, alcohols have long been used as renewable fuels and fuel additives such as, for example, octane boosters in gasoline formulated fuels. In 2011, world ethanol production for fuels reached 22.36 billion US gallons with the United States as the top producer at 13.9 billion US gallons. Alcohol-based additives including methanol (derived from natural gas), and ethanol (derived from bio-mass sources) offer relatively high blending octane numbers, competitive pricing and ample availability.
Energy-volume densities of alcohols are generally much lower than gasoline. For example, the energy-volume density of methanol is about 18.6 MJ/L, while gasoline is about 34 MJ/L. Although methanol's energy-volume density is relatively low, the energy-volume density of alcohols increases with increasing molecular weight of the particular alcohol. Higher alcohols such as, for example, ethanol and butanol have energy-volume densities of about 24 MJ/L and 29.2 MJ/L, respectively. If adequate supplies of ethanol, as well as mixtures of higher alcohols, can be made available, such higher alcohols can be utilized extensively on a wider scale, particularly as an alternative fuel, as well as booster additives for both octane and cetane fuels.
Since the early 20th century, catalysts have been formulated to produce mixtures of methanol and higher alcohols from syngas (a gas mixture composed of hydrogen and carbon monoxide). Certain catalysts formulated for synthesizing hydrocarbons from syngas were later discovered by Fischer and Tropsch (FT) to produce linear alcohols as by-products when impregnated with alkali impurities. This discovery eventually led to the development of other FT catalysts and alkali-doped zinc oxide/chromium (III) oxide catalysts capable of higher alcohol synthesis (HAS). During the late 1940's, the discovery of high yield oil fields diminished commercial interest in synthesis of alcohol from syngas.
Recently, in the face of rising crude oil costs and the nation's increasing reliance on foreign sources of oil, the Energy Independence and Security Act of 2007 was passed requiring the total amount of renewable fuels added to gasoline formulations be raised to 36 billion US gallons by 2022. These considerations have resulted in renewed interest and research in the synthesis of higher alcohols (HA) including ethanol.
Thermochemical conversion of biomass to ethanol and higher alcohols seems to offer an attractive and promising source of renewable energy. This process includes converting biomass into syngas, and then catalytically converting syngas to ethanol and other higher alcohols. Plentiful biomass, particularly agricultural and forest refuse, municipal solid waste, landfill gas, and the like, represent a potential source of syngas. Such biomass-based sources of renewable energy are expected to play an increasingly important role in the synthesis of clean, sustainable fuels and fuel additives.
Accordingly, there is a need in the art to develop a catalyst composition and method of using the same with enhanced productivity and selectivity for synthesis of an alcohol from synthesis gas. There is also a need for a catalyst composition and method of using the same characterized by long term stability, reduced water formation and other undesirable by-products, and being relatively easy to make and implement at lower costs.